Sport or athletic shoes have been anatomically improved not only to guarantee a better performance with higher stability of a sportsman's movements but also to provide them more protection to their body support parts which are constantly under high stress and impact pressure.
To better absorb any impact at the heel area of a shoe, a known solution is to place one or more damping pieces into a cavity located at the inner part of the sport shoe, that is, in its insole at the area of the heel, which will absorb impacts applied to the heel.
Solution for sport shoes with soles suggest in the case of soft soles made of elastic synthetic material, the placement of one or more replaceable pieces having a greater hardness than that of the sole into a cavity at the heel area. This makes possible a graduation of the flexibility reduction of the sole and a graduation of the shock adsorption capacity at this area in accordance with the individual characteristics of the sportsman and the sport.
One of the solutions is the use of one or more cylindrical or annular discs made of a material which is harder than that of the insole and has areas of different hardnesses. These are placed into direct contact with the inner surfaces of the insole cavity which, being of a normally very soft material prevents the movement of the parts inserted in this area. insole cavity may also be provided with a central axial pin the same insole material over which the annular shaped discs fitted. This assembly is covered by an insole of the sport and helps the discs to be retained by the heel pressure. When the insole is raised, the disc can be removed by pullers (for instance ribbons) attached to the parts.
However, in the case of sport shoes with a sole made of relatively solid or hard elastic synthetic material, the insertion of a flexible material which is softer than that of the insole into a cavity at the heel area allows for flexibility graduation of the sole at this area in addition to absorbing impact and returning power to the heel area. An existing solution in this case is the use of a damping element, also being power restoring, in the shape of only one tubular piece made of flexible material defining an air pressurized inner chamber under a predetermined pressure. The user can fit and remove the damper into a cavity provided in the sole of the sport shoe at the heel area.
The retention of the damping element inside the cavity is provided by direct contact of the walls thereof with the side surface of the damping element. This solution does not allow any intermediary combinations of damping/impulse adjustment, which are readily obtained by means of a set of independent dampers combined to act together. Also the whole damper piece wears, not necessarily in a uniform way, by the direct friction of the hard walls of the cavity in the insole with the side surface of the damper during the axial elastic deformations to which the damper is subjected while the shoe is used.
The use of a plurality of damping discs with variable hardness which is much lower than that of the insole, and therefore, that of the inner walls of said insole, would allow that from a certain number of damping discs a larger variation with more precision in the flexibility of the sport shoe is obtained than that which would be obtained with the same number of air pressurized damping elements. However, the arrangement of a plurality of damping discs directly located inside the inner cavity at the heel area of a hard insole material is not adequate due to the fact that there discs have more friction with the inner walls of the cavity, causing an irregular and high degree of wear of the disc, loss of power to be returned and poor distribution of the compression force of the heel through the discs overlapped inside the cavity. Such an arrangement also impairs the compressed air to be ejected by the heel, therefore causing the temperature and moisture to increase at the heel area and further making it difficult for the user to put the discs into and remove them from the cavity.